Thyroid hormone receptors are being studied in rat liver nuclei. The interaction of the hormone receptors with chromatin is the major thrust of our current studies. Nuclei will be incubated with micrococcal nuclease to generate nuclease resistant and sensitive chromatin fractions. These chromatin fractions will be analyzed for histone, nonhistone, and RNA content. Thyroid hormone receptor binding will be investigated in these nuclease generated chromatin subpopulations.